A phosphor is a luminescent material that absorbs radiation energy in a portion of the electromagnetic spectrum and emits energy in another portion of the electromagnetic spectrum. Some phosphors may require, or benefit from, the addition of small quantities of other elements, called “activators”, that can convert the phosphors into more efficient fluorescent materials. Further, combinations of activators and host compounds can be used to control the color of the emission. As such, phosphors find use in flat panel plasma displays, cathode ray tubes, x-ray imaging devices, field emission devices, fluorescent lighting fixtures, light emitting diodes and a variety of other applications to generate visual images or simply provide light.
However, many phosphors have poor environmental stability that makes their use in some of these applications impractical. The most common causes of this lack of stability are hydrolysis from water vapor exposure and carbon dioxide absorption of basic metal oxides.
And so, phosphors may typically be coated with a coating that prevents these gases from contacting the phosphor surface, allowing these phosphors to be industrially useful. For example, polymers have been used to coat phosphors, and although such polymer coatings may slow the movement of gas to the phosphor surface, polymers have very open structures compared to the size of gas molecules. As a result, diffusion still occurs.
Inorganic oxide coatings were thus developed, and may typically be applied by chemical vapor deposition, physical vapor deposition or from a liquid organometallic precursor. However, the applicability of these processes depends on the processing conditions and the chemical compatibility of the phosphor with the chemical precursors. That is, these coatings may react with the phosphor, resulting in a degradation thereof. And, such coating techniques require the use of expensive vacuum equipment, which may be cost prohibitive in some applications
It is thus desirable to provide phosphor coatings that can reduce or substantially prevent the degradation of the phosphor that can otherwise result from exposure of the phosphor to water vapor or carbon dioxide. Any such coating will also desirably be substantially inert to the underlying phosphor. The advantage of any such coatings could be further leveraged if their application did not require the use of expensive vacuum equipment.